Implement class deduction guides for `std::array`

[mclow.lists]

Summary

According to http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0433r2.html

Once this is reviewed, I'll do the rest of the sequence containers.

[EricWF]

include/array

75

Don't we normally comment // C++17 or similar for new features in the synopsis?

361

The is same clause is a requirement, not a SFINAE constraint. Should this be a hard error? Should we really SFINAE it?

test/std/containers/sequences/array/array.cons/deduct.fail.cpp

12

This should be UNSUPPORTED. We don't expect this test to ever pass without deduction guides.

test/std/containers/sequences/array/array.cons/deduct.pass.cpp

12

UNSUPPORTED

[mclow.lists]

include/array

75

we do.

361

If we SFINAE it, then we'll get a hard error; because there are no other deduction guides.

test/std/containers/sequences/array/array.cons/deduct.fail.cpp

12

OK

[mclow.lists]

Committed as revision 332768

[yroux]

Hi Marshall,

ARM and AArch64 libcxx buildbots are broken since that commits, logs
are available at:

http://lab.llvm.org:8011/builders/libcxx-libcxxabi-libunwind-armv7-linux/builds/107/steps/test.libcxx/logs/FAIL%3A%20libc%2B%2B%3A%3Adeduct.pass.cpp

Thanks
Yvan

include/array

     const T* data() const noexcept;
 };
 
+  template <class T, class... U>
+    array(T, U...) -> array<T, 1 + sizeof...(U)>;
+
 template <class T, size_t N>
   bool operator==(const array<T,N>& x, const array<T,N>& y);
 template <class T, size_t N>

 };
 
 
+#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
+template<class _Tp, class... _Args,
+         class = typename enable_if<(is_same_v<_Tp, _Args> && ...), void>::type
+         >
+array(_Tp, _Args...)
+  -> array<_Tp, 1 + sizeof...(_Args)>;
+#endif
+
 template <class _Tp, size_t _Size>
 inline _LIBCPP_INLINE_VISIBILITY
 bool

test/std/containers/sequences/array/array.cons/deduct.fail.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <array>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// XFAIL: libcpp-no-deduction-guides
+
+
+// template <class T, class... U>
+//   array(T, U...) -> array<T, 1 + sizeof...(U)>;
+//
+//  Requires: (is_same_v<T, U> && ...) is true. Otherwise the program is ill-formed.
+
+
+#include <array>
+#include <cassert>
+#include <cstddef>
+
+#include "test_macros.h"
+
+int main()
+{
+    {
+    std::array arr{1,2,3L}; // expected-error {{no viable constructor or deduction guide for deduction of template arguments of 'array'}}
+    }
+}

test/std/containers/sequences/array/array.cons/deduct.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <array>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// XFAIL: libcpp-no-deduction-guides
+
+
+// template <class T, class... U>
+//   array(T, U...) -> array<T, 1 + sizeof...(U)>;
+//
+//  Requires: (is_same_v<T, U> && ...) is true. Otherwise the program is ill-formed.
+
+
+#include <array>
+#include <cassert>
+#include <cstddef>
+
+#include "test_macros.h"
+
+int main()
+{
+    {
+    std::array arr{1,2,3};
+    static_assert(std::is_same_v<decltype(arr), std::array<int, 3>>, "");
+    assert(arr[0] == 1);
+    assert(arr[1] == 2);
+    assert(arr[2] == 3);
+    }
+
+    {
+    std::array arr{1L, 4L, 9L, 16L};
+    static_assert(std::is_same_v<decltype(arr)::value_type, long>, "");
+    static_assert(arr.size() == 4, "");
+    assert(arr[0] == 1);
+    assert(arr[1] == 4);
+    assert(arr[2] == 9);
+    }
+}